1. Field
The inventive concept relates to a distributed antenna system, and more particularly, to a distributed antenna system for time division duplex (TDD).
2. Description of Related Art
As wireless multimedia services, social networking services (SNS), internet of things (IoT), and the like come into wide use due to the spread of smartphones, the demand for wireless data traffic is explosively increasing. A big data environment has emerged which is not easily processed by using the existing data transmission method. Accordingly, a distributed antenna system (DAS) in which one master unit (MU) linked with base stations can control remote units (RUs) that are a plurality of antenna modules connected to the MU through an optical cable is used to efficiently manage wireless resources.
Meanwhile, in recent wireless mobile communication, a technique using time division duplex (TDD) as a duplex scheme has been widely used. Here, the TDD refers to a bidirectional transmission scheme in which uplink and downlink are alternately allocated in the same frequency band according to time sequence. The TDD has higher transmission efficiency than frequency division duplex (FDD) in which different two channels are allocated to the uplink and the downlink.
A conventional relay to which the TDD is applied should have a function of controlling a switch to perform a switching operation between downlink and uplink periods by analyzing a transmission signal frame. U.S. Pat. No. 8,208,414 discloses, as an invention related to a relay to which the TDD is applied, a method of controlling a switch as a master unit (MU) detects a downlink signal received from a remote unit (RU). According to U.S. Pat. No. 8,208,414, the MU requires a control signal for accurately distinguishing a start point of a downlink signal from a start point of an uplink signal and controlling opening/closing of the switch in response to each signal, thereby changing a transmission path of the signal.
In the conventional distributed antenna system, the MU requires a switch for alternately allocating uplink and downlink and a controller for controlling the switch, and hence a malfunction may occur due to defects of the switch and the controller. Also, the switch and the controller are relatively high-priced components, and hence the manufacturing cost of the relay is increased.